Background music in shops - disparagingly referred to as "muzak" - has been shown to have an effect on our buying habits.

Shops and restaurants can use music "to target those effects that are most likely to increase sales in a given business", says Adrian North, professor of music psychology at Australia's Curtin University in Perth.

His own research, carried out at Softley's restaurant in Market Bosworth, Leicestershire, suggested diners spent an average of £2 a head more when listening to classical rather than pop music.

A similar experiment suggested that perceptions of taste altered according to output, so "mellow and soft music"- made the wine taste "mellow and soft". And "powerful and heavy" sounds, made wine more likely to have flavours that were... "powerful and heavy".

What is muzak?
Muzak started in 1920s when General George Squires patented the process of transmitting music over electrical lines. The name is a combination of "music" and "Kodak", Squires' favourite hi-tech firm. It is known as "elevator music" because of its early use in skyscrapers to calm people's nerves (when elevators were still new and unfamiliar). In the 1940s, it was used as a musical way of relaxing workers with the aim of improving productivity.

Muzak has a reputation as being generic, light music, barely noticeable to customers - setting a calm ambience in which to buy things. But the Muzak company that gave rise to the term, taken over by Canadian firm Mood Media in 2004, tailors its playlists to target specific groups of customers, as do several large rivals.

In his BBC Reith Lectures 10 years ago, conductor and pianist Daniel Barenboim complained that background music was undermining "active" listening, creating a generation of people who could no longer concentrate properly on music.
Research at Rutgers University at about the same time suggested music played in shops had no discernible impact on customers' stated mood. But, while it did encourage higher levels of spending among impulse buyers, "contemplative" shoppers actually spent less.

Defenders of in-store sound say it is no more manipulative than other aspects of store design and management, such as layout, decoration and product presentation.

North says there's evidence that playing Edith Piaf's songs encourages people to buy French wine, rather than South African. "And we know that classical music can drive sales of more expensive products," he says, "whereas country [music] drives sales of utilitarian products."

A few years ago, music writer Paul Stokes attempted to log the songs he heard while shopping in London, but gave up because "it was all either faceless audio wallpaper, or the same pop hits of the day produced by Pharrell Williams".

"Experts say you should only notice the music one in three tracks," he says. "The rest of the time it was there to provide a sense of comfort and calm."